In most bone or joint arthroplasty, replacement and/or reconstruction surgery procedures, a bone or a joint is replaced by a prosthetic implant. The main goal of an arthroplasty intervention is to relieve (arthritis) pain or to restore severe physical joint damage resulting from, for example, trauma. When a prosthesis fails, a revision arthroplasty is carried out. This procedure is technically more difficult and time-consuming than the primary intervention and the outcome is often less satisfactory, both because there is less bone stock to work with and because the removal of adherent cement or prosthetic components may result in fracture or perforation of the bone. With each successive joint revision, the risk of infection and symptomatic loosening of the prosthesis may increase substantially. Revision surgeries become more frequent as the population grows older and patients receive prostheses at an earlier age.
The treatment of bone and joint defects has gradually become more complex. While it started out with standard interventions using off-the-shelf prosthesis components, it has evolved to patient-specific surgery plans and patient-specific implant designs. The accurate and stable fixation of implants onto the bone or joint, while increasingly difficult, remains one of the most important steps in arthroplasty interventions.
The standard process of fixing or anchoring an implant with screws into the bone is mostly a two-step procedure. First, the screw trajectory is pre-drilled with a dedicated instrument. This is followed by the screw insertion along the pre-drilled screw trajectory. Some self-tapping screw types do not require pre-drilling; direct insertion of the screw, directly establishes the screw trajectory.
Unfortunately, this anchoring process has a number of important drawbacks.
Indeed, deviations in direction and/or location of the screw trajectory often lead to a suboptimal screw traction which may cause soft tissue damage. The pre-drilling and/or placing of the screws are often done by the surgeon free-hand style, with only a limited view on the bone through the available surgical incision. Moreover, where the surgeon has sufficient exposure of the patient and a wide view on the implant and screw hole and is able to orient the pre-drilling instrument in any orientation (which is not often the case), he will typically use the surface curvature of the implant around the screw hole as a visual reference and will aim at placing the instrument orthogonally with respect to the local implant surface. As a result, the obtained screw directions are often suboptimal and/or deviate from a preoperative plan. Screws can for example be directed in bone of low quality, or have only limited traction length. In addition, a shift of the implant away from the optimal location before pre-drilling has started can cause screw locations, i.e. insertion points of the screw trajectories into the bone, to deviate from a predetermined location.
Deviations in the direction and/or location of a screw trajectory may also cause the screws to become mutually intersecting, causing e.g. the insertion of a first screw (either with or without a planned direction) to block the insertion of the next. Unused screw holes badly influence the implant's long-term integrity, unless some other portion of the implant compensates the local decrease in material volume. This however implies the use of more implant material, for example thickening of the implant, making it more bulky, and/or requires larger contact regions with the bone. The latter again is detrimental to soft tissue preservation.
Specific tools and technologies have been developed in the past in order to solve the above problems associated with the fixation or anchoring process of the implant.
Navigation technology has for instance been used as a global positioning system for the surgeon. For example, infrared sensors placed near the bone or joint in the operating room act like satellites constantly monitoring the location of markers and instruments placed along a patient's anatomy. Unfortunately, this technology is expensive and intra-operatively very time-consuming.
A system for fixation of an implant onto a bone is provided in U.S. Pat. No. 7,153,309 (Huebner et al.), in which a guide device is attached to a bone plate. The use of this device is in practice however limited to anatomical areas which can be extensively exposed or can be easily approached from different directions. For example, the device does not allow pre-drilling from the ipsilateral side of a bone plate, a procedure which is however often needed, for example in implant surgery of the hemi-pelvis, scapula, or mandible. US2008/0183172 describes a guide for a bone plate which is more compact but similarly comprises a projection extending from the guide which is configured to be received within an aperture in the bone plate for securing the plate guide to the plate. The aperture can be a bone-screw receiving aperture inherently present on existing bone plates or an aperture designed to receive a projection comprising a resilient finger. These devices can however only be applied in cases of bone repair (following traumata, with multiple bone fragments), and not for bone and joint repair such as in arthroplasty. In addition, the described plate-guide fixation systems define the direction and insertion point of a connective feature with respect to the plate, and (only if the plate is patient-specific) also with respect to the bone. Accordingly, absolute referencing, needed to transfer a preoperative surgery plan on the patient bone geometry and derived from medical images onto the patient's bone during surgery, is not guaranteed. Finally, the guides are physically attached to the plate, requiring attachment features on both components and moreover requiring assembly manipulations.
Standard-size drill guiding cylinders have been described, which can be screwed into the implant screw hole (such as for example for the Compliant Pre-Stress (CPS) device of Biomet Inc.; Warsaw, Ind.). Due to reasons of manufacturability, machine set-up time and costs, this guiding solution is limited to large series of off-the-shelf implants, for which it is economically profitable to set up expensive threading machinery.
Patient-specific bone guides have a unique (partial) fit with a portion of the surrounding bone, and therefore allow the guiding of features, such as bone drilling and/or cutting elements, in an unambiguous and accurately planned trajectory or direction into the bone (Tardieu P B (2007) Int. J. Periodontics Restorative Dent. 27(2): 141-149; Kunz M (2007) Proceedings of the 7th Annual Meeting of CAOS-International: 159-161; Lombardi Jr A V et al. (2008) BFA Orthopedics; 31: 927). However, a custom bone guide is not always a guarantee for adequate implant fixation, especially in the case of a patient-specific implant. For certain anatomical regions, and especially in complex revision cases, the only bone regions which can be exposed and reached through the surgical window are few, small and spread out. One could think of a patient-specific implant reaching out to these regions for fixation. Pre-drilling screw holes could be performed with a plastic implant replica serving as a base frame for the bone guides. This is however unpractical and ineffective since the guide-frame construction has to be taken out, and the implant reinserted while keeping track of the pre-drill locations. Furthermore, the use of a Kirschner wire to keep track of the pre-drill locations while sliding off the guide and sliding the implant on is not convenient and not fully constrained.
Accordingly, there is a need for alternative and improved (customized) surgical guides, which are stable and which provide the ability to accurately insert a surgical instrument into a patient's bone or joint.